AM625: OLDI interface impedance

Hello Tony,

Thank you for the query. I assume you are checking about OLDI interface

7.11.5.17 OLDI
7.11.5.17.1 OLDI0 Switching Characteristics

Does the data sheet specs help.

I need to check with the expert on the reason for not including the OLDI impedance based on your confirmation.

Regards,

Sreenivasa

Hello Sreenivasa,

the switching characteristics is timing relevant. 

Customer asks for impedance. There is notes under the table, need to be clarified.

#1. Does it need to terminate with pararell 100ohm resistor on OLDI pairs on schematic?

#2. On SK-AM62 schematic, highlighted the impedance be 100ohm, but did not add real100ohm resistor.

Hello Tony, 

Thank you for the inputs.

Tony Tang said:

On SK-AM62 schematic, highlighted the impedance be 100ohm, but did not add real100ohm resistor.

The marking is the trace impedance.

Tony Tang said:

Does it need to terminate with pararell 100ohm resistor on OLDI pairs on schematic?

Is your questions is on the SoC side, this may not be required.

Regards,

Sreenivasa

Hello, Sreenivasa,

How to interpret the notes, and how to deal with it in schematic design?

Hello Tony, 

Thank you. 

As i understand these are the configurations for slow and fast mode

(1) Slow mode: TXDRV[3:0] = 0100b without back termination (RTERM_EN = 0b with 100Ω differential termination on far-end only)
(2) Fast mode: TXDRV[3:0] = 1000b with back termination (RTERM_EN = 1b with 100Ω differential termination on far-end only, or

This is the case where internal back termination is off and external termination on the board is placed.
RTERM_EN = 0b with 100Ω differential termination on near-end and far-end) 

The far end termination may be inside or outside and that depends on the attach device.

Is your question if 100 R is required to be placed on the SOC board?

Regards,

Sreenivasa

Hello Tony, 

Please refer below thread if that helps.

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1273263/am625-oldi-voltage-swing-and-rise-fall-time/4836261?tisearch=e2e-sitesearch&keymatch=OLDI%20100#4836261

Regards,

Sreenivasa

Hello, Sreenivasa,

Okay, now I understand the SOC internal termination(back termination) is optional to disable and enable. 

The back termination enabled in default, so no need external 100ohm termination?

From the thread's experience, reserve a far end termination pad would be flexible to adjust?